Heterochromatin formation is essential for chromosome segregation, epigenetic silencing and X chromosome inactivation. In spite of their biological significance, the mechanisms involved in the establishment of heterochromatin domains during oogenesis are currently unknown. The focus of this proposal will be on two members of the SWIISNF2 family of chromatin remodeling proteins Lsh and A TRX known to have a role in DNA methylation. This proposal is based on the following hypotheses 1) that Lsh is essential for genomic stability during female meiosis;and 2) that both ATRX and Lsh are essential for centromeric heterochromatin formation and epigenetic gene silencing during mouse oocyte growth. The specific objectives include (1) To determine the role of the lymphocyte specific helicase (Lsh) during prophase I of meiosis;(2) To determine whether the Lsh protein has a functional role in centromeric heterochromatin formation during mouse oocyte growth. A transgenic knockout mouse model will be used to determine the mechanisms interfering with homologous chromosome synapsis in Lsh null oocytes during prophase I of meiosis. Particular emphasis will be placed to characterize the molecular interactions between Lsh and ATRX during oogenesis and to determine their functional significance for centromeric heterochromatin formation. These studies will provide critical information regarding the relationship between DNA methylation, heterochromatin formation and epigenetic gene silencing during female meiosis, as well as the mechanisms affecting meiotic centromere function, genomic stability and the molecular mechanisms contributing to the onset of aneuploidy in the mammalian oocyte and pre-implantation embryo.